Transient protection units of the above-indicated kind are intended to suppress dynamic variations in conductors generated by NEMP and LEMP (i.e., electromagnetic pulses arising from nuclear missile explosions or lightening and) also electromagnetic interference (EMI). In the case of pulses arising from nuclear missile explosions, there may be maximum values in the order of magnitude of 50 kilovolts with rise times in the order of magnitude of 5 ns. For effectively leading away as large a part as possible of such a pulse, associated gas discharge tubes should have a very low inductance to ground.
The secondary protection part is intended and dimensioned for catering to the remainder of the original pulse, which does not manage to be led to ground, and which may have an amplitude in the maximum order of magnitude of 1200 volts. It is important for the secondary protection part that there is as good screening outwardly as possible. In some cases, this requirement has been found inconsistent with the requirement for low inductance to ground of the gas discharge tubes.